Once the
printed circuit board (PCB) is complete,
electronic
components must be assembled to form a functional printedcircuitassembly, or PCA or PCBA (printed circuit
board assembly).

In through-hole PCA, component leads
are inserted in holes and thus the name Thru-Hole. In
surface-mount PCA, components are placed on pads or lands on
the outer surfaces of the PCB.

In both kinds of assembly
(Thru-Hole and
SMT), component leads are electrically and
mechanically fixed to the board with solder. In case of
Thru-Hole,
solder wire or solder bar is used while in SMT,
solder balls of solder paste is used.